1. Field Of The Invention
The present invention relates to a method and well casing and more particularly to such a method and well casing which substantially improve upon the productivity of which a well is capable ensuring that the well can be operated with an efficiency considerably beyond that which has heretofore been possible and having particular utility in fluid recovery from two or more fluid bearing formations simultaneously.
2. Description Of The Prior Art
A primary objective in the operation of wells of all types and particularly deep water wells is maintaining well production at the desired level. Another primary objective is reducing to a minimum the power required to maintain a given level of productivity for a well. In water wells, for example, it is known that where the aquifer is not sufficiently pressurized, it is extremely expensive to pump water from the well. This problem is compounded where the structure of the fluid bearing formation and/or the gravel pack about the well casing interefere with the influx of water from the upper portions of the aquifer. Where these conditions exist, productivity rapidly drops off and the cost of operation increases.
It has been found in these and other situations that, using conventional procedures, it is necessary to elevate or lower the pump assembly in the well to reposition the intake at a level such as to permit more efficient extraction from the specific fluid bearing formation involved. This can be extremely expensive and in some instances prohibitively so.
Another problem encountered in well operation exists where there are two or more superimposed fluid bearing formations. The formations are usually separated from each other by impervious rock strata. In a conventional casing if perforations were provided to communicate with more than the lower formation, fluid entering the perforations from the upper formations would entrap air. Such air causes rapid wearing of the pump and eventual destruction of it. It can also cause a pump assembly to lose its priming. Since this is unsatisfactory and since there is in such a condition little or no communication between the formations outside the casing, the formations must be tapped individually. This requires repositioning of the pump assembly within the well after one formation has been exhausted. Insofar as the applicant is aware, it has not heretofore been possible as a practical matter to pump simultaneously from two or more formations other than as may incidently occur from percolation from the upper formations to the lower formations. Such percolation is of an inconsequential amount and does not, as a practical matter, permit utilization of such upper formations.
Therefore, it has long been known that it would be desirable to have the capability of maintaining well productivity at a high level while minimizing the energy requirements for maintaining such a level of production and it has further been known that it would be desirable to be able to pump from two or more fluid bearing formations simultaneously without modification or repositioning of the pump assembly and without destruction of the pump assembly as a result of entrapped air.